This invention relates to compositions useful in making low dielectric constant insulating layers in microelectronic devices.
As semiconductor devices become smaller and smaller, and chip packing densities increase correspondingly, undesirable capacitative delays and crosstalk between metal interconnects are more acutely manifested. There has been a movement away from using silicon dioxide with a dielectric constant of about 4.2 to benzocyclobutene based polymers (BCB), such as CYCLOTENE(trademark) resins from The Dow Chemical Company, and polyarylene resins, such as those disclosed in WO98/11149, both of which have dielectric constants of about 2.6. Since capacitative delays and crosstalk relate to the dielectric constant of the insulator, additional attention has focused on the creation of ultra-low dielectric constant materials (that is, dielectric materials having dielectric constants of xe2x89xa62.0). Such efforts include creating porous inorganic (for example, silicon dioxide) or thermoplastic polymeric (for example, polyimide) materials.
Silicon dioxide, which has been the dominant interlevel dielectric material (ILD) for the past 40 years, can be made porous by well developed sol-gel techniques such as those disclosed in Proc. Mat. Res. Soc. 381, 261 (1995); Proc. Mat. Res. Soc. 443, 91 (1997); and Proc. Mat. Res. Soc. 443, 99 (1997). The inorganic networks which form are highly cross-linked and exhibit substantial modulus at early stages of their formation utilizing relatively low temperature processes. Although the introduction of pores into silicon dioxide causes a reduction of dielectric constant from 4.2 to less than 2.0, the resultant porous material is significantly weakened and the porous coatings are easily damaged during handling and during the processing steps necessary to fabricate microelectronic devices. Thus, porous silicon dioxide is impractical as an ultra-low dielectric constant material.
Porous thermoplastic polymers, particularly thermally stable polymers such as polyimides, have also been investigated for use as ultra-low dielectric constant materials. Although these porous thermoplastic materials can be made to have acceptable dielectric constants and are relatively tough, being able to withstand the mechanical processing steps necessary to fabricate microelectronic devices, the pores tend to collapse during subsequent high temperature processing due to the modulus drop associated with being above the glass transition temperature of the resin, thereby precluding the use of these materials for the applications of interest.
The initial proposals for developing porous layers generally involve adding a pore generating material, also referred to as a poragen, to a composition comprising a matrix precursor, forming the matrix from the precursor, and then degrading the pore generating material, to form pores in the matrix material.
Applicants have discovered that despite being thermosetting resins, certain of the polyarylene resin formulations disclosed in WO98/11149 may suffer from pore collapse when attempting to form a porous structure from the resin by introduction of a poragen into the b-staged formulation, curing and removal of that poragen. This is believed to occur because the poragen degrades before the matrix has sufficiently set. Modifying the formulation so that the resin does not undergo a significant drop in modulus during cure or alternatively shifting the temperature at which the minimum modulus occurs to a lower temperature, enables one to avoid pore collapse and/or use a wider variety of poragen materials.
Thus, according to a first embodiment, this invention is a composition comprising a partially polymerized reaction product of a reaction mixture comprising a compound having two or more cyclopentadienone functional groups and a compound having three or more acetylene functional groups, wherein the composition is further characterized by one or more of the following characteristics:
(a) the ratio of cyclopentadienone groups to acetylene groups in the reaction mixture is at least about 3:4 and, preferably no greater than 2:1, more preferably the ratio is in the range of 9:10 to 10:9, and most preferably the ratio is about 1:1;
(b) the compound having three or more acetylene functional groups is selected from the group consisting of tris(phenylethynyl)diphenyl ethers, tris(phenylethynyl)-ortho-terphenyls, 4xe2x80x2,4xe2x80x2,4xe2x80x2-tris(phenylethynyl)-1,3,5-triphenylbenzene, and 3xe2x80x2,3xe2x80x2,3xe2x80x2-tris(phenylethynyl)-1,3,5-triphenylbenzene;
(c) the reaction mixture further comprises a compound which has the ability to react with non-functionalized aryl groups;
(d) the composition further comprises a reagent selected from the group consisting of bis-ortho-diacetylenes, mono-ortho-diacetylenes, bistriazenes, tetrazines, bisazides, bissulfonylazides and peroxides. Preferably, the composition comprises a solvent and most preferably also comprises a poragen.
According to an alternative embodiment, the invention is a composition comprising precursor compound(s) which when cured form a polyarylene material wherein the composition has a modulus profile as measured by torsional impregnated cloth analysis (TICA) characterized in that during heating of the composition a minimum measured modulus observed in the temperature range from 250 to 450xc2x0 C. occurs at a temperature Tmin, and said minimum measured modulus is greater than a value equal to 20 percent of a measured cured modulus of the composition after heating to a maximum temperature and cooling back down to Tmin. According to a third embodiment, the modulus profile is characterized by having a modulus at 388xc2x0 C. during heating of the composition which is greater than a value equal to 20 percent of a measured cured modulus of the composition at 388xc2x0 C. after cure. The invention is also a mixture comprising the composition of the second or third embodiments and a solvent, and preferably, a poragen.
Finally, the present invention is a method of making a film comprising coating one of the above compositions onto a substrate, removing the solvent, and curing the resin. Preferably, the composition further comprises a poragen and the method includes a step of removing (e.g. by decomposition) the poragen. The solvent removal, curing, and removing (decomposition) steps may occur separately in stages or may be accomplished by a single heating step. The present invention further includes an article comprising the film made in accordance with the seventh embodiment. Preferably, the article is an integrated circuit article.